No, it's impossible.
In the CMI scripts there are no symbol names stored, just plain numbers.
In EMI and Grim Fandango you can see all function and variable names because they use the open-source Lua scripting language (www.lua.org) which stores all symbol names in the script files.

Of course it's not a total loss - you can see what the major ones are by looking at scumm/vars.cpp in the ScummVM source (search for Scumm_v8::setupScummVars). Of course if you were using ScummVM's descumm utilities, it should automatically label these variables anyway.

Stuff thats strictly game puzzle related, you'd have to guess, or try and bug Serge for his personal varnames.ini

Yeah, VarNames.ini is the mapping file for CMIDec (of course)... but the only ones I've seen are very incomplete.

I know Serge must have a slightly larger version, because I've seen decompiled scripts from him with named variables. Unless he didn't use his own programs feature, and added them in by hand for posting

I did. I think I had a list of about 20-30 varnames and guesses at varnames. Didn't add the rest, since they were non-engine variables and I wasn't sure if they were used for different purposes in different scripts. Never got down to checking, so...